Synthesis And Properties Of Supramolecular Crosslinked Polyacrylic Acid/Acrylamide Hydrogels

In recent years,supramolecular gels have gradually developed into a class of functional materials with broad application prospects.The supramolecular gels based on host-guest molecular recognition,hydrogen bonding and so on have been widely studied among them,but the research on the construction of supramolecular gels by coordination bonds is sufficient.In this dissertation,three kinds of copolymers by 4-?2,2':6',2"-terpyridine-4'-yl?styrene?TPY?as the center,and acrylic acid?AA?and acrylamide?AM?as hydrophilic monomers were prepared and complexed with transition metal ions to obtain metal supramolecular hydrogels.The structure and properties of hydrogels were characterized and discussed in detail.1.TPY monomer was synthesized by Krohnke synthetic route.PAT was synthesized with acrylic acid?AA?and TPY.The monomer 9,9-dioctyl-2-vinylindole?OVF?was designed and synthesized.PATF was synthesized with AA,TPY and OVF.The metal supramolecular hydrogel was prepared by the copolymers which have both water solubility and coordination with metal ions.All of the obtained intermediates,monomers,and copolymers were structurally characterized by ¹H NMR,infrared.The molecular weight of the copolymer was determined by the viscosity method.The results showed that as the content of TPY and OVF increased,the molecular weight of the copolymer decreased and the hydrophobicity increased.After hydrolyzing PATF to a dilute solution,it is mixed with different concentrations of transition metal ions such as Ni²⁺,Fe²⁺,Zn²⁺,Cd²⁺,and subjected to ultraviolet-visible light test and fluorescence test.According to the ultraviolet absorption spectrum analysis,after adding metal ions such as Ni²⁺,the absorption peaks have different degrees of red shift,and there is a linear relationship between the absorption peak and the absorption intensity and the ion concentration,which can be used for the detection of transition metal ions in aqueous solution.Fluorescence spectroscopy showed that Fe²⁺ and Ni²⁺ have quenching effect on fluorescence,and ligands with Cd²⁺ and Zn²⁺ have obvious fluorescence.Through the rheological test,compression test and scanning electron microscopy analysis of the obtained metal supramolecular hydrogel,it was found that different ions and their concentrations and the water content of the polymer have different effect on the formed of gel,rheological behavior,mechanical strength and surface morphology of the gel.2.PAMT was synthesized by TPY with acrylamide?AM?.All of the obtained intermediates,monomers,and copolymers were structurally characterized by ¹H NMR,infrared.The molecular weight of the copolymer was determined by viscosity method.The result showed that the molar addition of TPY in the copolymer was increased from0.4% to 1%,and the viscosity molecular weight was decreased from 2.02×10⁵g/mol to 1.63×10⁵ g/mol.This is because the benzene ring in the TPY monomer and the terpyridine group have a very large steric hindrance,which lowers the molecular weight of the polymer.The analysis of the thermogravimetric curve of the copolymer showed that the thermal stability is good and it can be stably present in the water system.The copolymer was dissolved in water at a concentration and complexed with a transition metal ion to obtain a metal ion-induced supramolecular hydrogel.The rheological behavior and micromorphology of the supramolecular hydrogel were analyzed by rheometer and scanning electron microscope.The results showed that the storage modulus?G'?and loss modulus?G'?of the gel remain unchanged in the strain range of 0.1%-15%,which is its linear viscoelastic region;6 wt%,8 wt% and 10 wt% of the gel formed by the polymer,in the frequency sweep range,G'had a small increase,G'increased,and the modulus of the three increases with the polymer concentration increased.At the same time,the pH sensitivity of the gel was initially explored.It was found that the swelling ratio of the gel did not change much under acidic and neutral conditions,and the swelling ratio reached the maximum at pH=10.3.PNAMT was synthesized by copolymerizing TPY with N-isopropylacrylamide?NIPAM?and acrylamide?AM?.All of the obtained intermediates,monomers,and copolymers were structurally characterized by ¹H NMR,infrared.The molecular weight of the copolymer was determined by the viscosity method.The results showed that the molar molecular weight of NIPAM and AM in the copolymer decreased from 8:1 to 2:1,and the viscosity molecular weight increased from 1.48×10⁵ g/mol to 2.50×10⁵g/mol.This is because N-isopropylacrylamide has a large steric hindrance compared to the acrylamide unit,hinders the reaction between functional groups,and therefore has a small molecular weight.From the analysis of the thermogravimetric curve of the copolymer,the thermal stability is good and it can be stably present in the water system.The copolymer was dissolved in water at a concentration and complexed with a transition metal ion to obtain a metal ion-induced supramolecular hydrogel.The rheological behavior and micromorphology of the supramolecular hydrogel were analyzed by rheometer and scanning electron microscope.The results showed that the linear viscoelastic region of the gel is 0.1%-10%;as the scanning frequency increases,the G'and G'of the gel formed by the 8 wt% and 10 wt% polymers remain substantially constant,and the modulus of 10wt% is slightly higher than 8 wt%.At the same time,the temperature sensitivity of the gel was initially explored.It was found that the critical transition temperature in the aqueous polymer solution and its gel was mainly affected by the N-isopropyl acrylamide content.The LCST is increased compared to the polymer solution after the introduction of metal ions to form the supramolecular hydrogel.